In a Ninja Creami pint container, combine the crushed pineapple (with juice) and sweetener.
Add the milk and use an immersion blender to mix the ingredients well, ensuring they stay below the fill line.
Place the container on a flat, level surface in the freezer and freeze for 24 hours or until solid.
Once frozen, remove from the freezer and run the pint under hot water for 30 seconds before removing the lid.
Place the container into the outer bowl of the Ninja Creami and secure the outer bowl lid.
Lock the outer bowl into the Ninja Creami machine, press the Lite Ice Cream button, and let the cycle complete.
If the ice cream is powdery after the first cycle, add a splash of pineapple juice or milk and press the Re-spin button.
Scoop into bowls, top with extra pineapple if desired, and enjoy!